Cavitation is the occurrence of cavities (voids) in liquids in the form of bubbles where the liquid has transformed into a gas when the static pressure in the liquid has decreased. Cavitation is a mixture of gas formation, the release of trapped air in the liquid and the expansion of air bubbles contained in the liquid.
In cases where the cavitation bubbles implode when the static pressure increases, a very thin jet stream with large force can be formed from the bubble which can damage solid surfaces in the vicinity. A blister forms in a low pressure zone and adheres to a solid surface and implodes when the surrounding static pressure increases. The effect is the same as thousands of sharp nails hammering the surface with a large force whereby the material's ultimate tensile strength can be exceeded, which eventually gives rise to a visible loss of material, often leaving thousands of small craters in the material. This is a known phenomenon in hydraulic rock drilling machines.
Cavitation occurs for example in the area around the damper piston, i.e. the component that forces the adapter/drilling steel/bore crown against the rock so that joints can be tightened between impacts, when the damper piston moves forwards and thereby quickly increases the volume between the damper piston and the damper chamber or the machine body. This problem is usually combatted using a one way valve that fills the volume with oil in order to decrease the occurrence of cavitation bubbles (see U.S. Pat. No. 4,993,504). When the damper piston moves forwards, a substantial pressure decrease occurs which leads to cavitation if the oil cannot be replaced at the same rate as the volume increases. Cavitation bubbles therefore occur since the hydraulic pressure is low and the pressure decrease propagates through all hydraulically connected spaces. Oil starts to flow to the area with the lowest pressure from all possible directions. Cavitation bubbles can thereby spread to and/or also occur in places other than in the original space between the damper piston and the damper chamber (machine body. The low pressure causes the oil from surrounding spaces to flow to the low pressure area to re-establish mean pressure in the damper device. For this reason many drilling machines often have a damper accumulator so that a large volume of oil is readily available to even out the hydraulic pressure, but this is not sufficient to solve the cavitation problem. When the cavitation bubbles finally collapse there is an obvious risk that some of them will be located in the vicinity of sensitive components and will for example damage seals.